Seattle Mariners right-hand pitcher Hisashi Iwakuma will not throw for four to six weeks after injuring the middle finger on his throwing hand, according to an announcement Wednesday by Mariners GM Jack Zduriencik.

Dr. Don Sheridan, an Arizona-based hand specialist, examined Iwakuma and diagnosed the injury as a strained tendon in the middle finger. The finger has been placed in a protective splint and will be re-examined in three weeks.

According to Zduriencik, the injury does not appear to be serious and Iwakuma should be able to join Seattle’s starting rotation early in the regular season.

Even if it’s not serious, any health concerns for Iwakuma are sure to make Mariners fans uneasy. Iwakuma had a fantastic season last year, going 14-6 with a 2.66 ERA and a 1.01 WHIP. He was named to the 2013 All-Star team and came in third in the Cy Young voting behind Detroit’s Max Scherzer and Texas’ Yu Darvish.

If Seattle’s pitching staff is to have any hope of being respectable beyond perennial ace Felix Hernandez, Iwakuma will have to be a major contributor.

Mariners pitchers and catchers reported to spring training Wednesday and are set to have their first workout Thursday.